In recent years, an image processing technology that analyzes an image acquired by an imaging apparatus to detect persons contained in the image is widely used. According to such an image processing technology, the number of persons passing through the entrance/departure gate can be counted by installing an imaging apparatus in the entrance/departure gate of, for example, a station, airport, amusement area, theater, hall or the like. In addition, as described in Patent Literature 1, person tracking can be realized by using image processing.
The face detection of a person will briefly be described here. The process of the face detection of a person mainly includes matching processing to verify whether each region in an image matches predetermined face patterns and analysis processing to analyze a matching region in detail by face authentication or the like. Because the size of a face in an image changes depending on the imaging distance of a person, the above matching processing is performed for face patterns of various sizes.
On the other hand, as disclosed in, for example, Patent Literature 2, a distance image sensor that generates a distance image representing the distance of each position in an object space is also under development. In the distance image sensor, for example, photoreceptors corresponding to pixels are arranged in a matrix shape. Then, the distance image sensor can measure the relative distance between an object having reflected light and the distance image sensor in each position corresponding to a pixel in the object space by radiating light and measuring the time needed for the light reflected by the object to return for each pixel.